Did you know that your chances of beating cancer depend on the season you are diagnosed in? It may seem bizarre but a large number of studies have found that individuals who are diagnosed with cancer in the summer have a better cancer prognosis than those diagnosed in the winter, apparently due to increased production of vitamin D by the body over the summer months.
A 2004 study, published in the journal Cancer Causes and Control, looked at the effect of sunlight on the prognosis of colon, breast, and prostate cancer in Norway. The researchers found that the case-fatality rate was higher in winter than in other seasons for all three forms of cancer. After adjustment for potential cofounders, three year case fatality rates in summer compared to winter were 21% lower for breast cancer, 20% lower for prostate cancer, and 15% and 20% lower for colon cancer in men and women respectively. The researchers concluded that “If [these findings] are conﬁrmed, in addition to traditional cancer treatment, vitamin D would be of particular importance in the primary prevention of death from the cancer types studied.”
A second study, published in the journal Cancer Epidemiology, Biomarkers & Prevention in 2005, found a similar link between non-small cell lung cancer and vitamin D levels. In that study, individuals who had both a low intake of vitamin D and had surgery in winter had 5 year recurrence free survival (RFS) rates of 23% compared to a 56% RFS for those who had both a high intake of vitamin D and surgery during summer.
While vitamin D is found in some foods, the easiest way to increase circulating vitamin D levels is through sun exposure. Unfortunately, during winter in countries at very high and low latititudes, UVB levels from the sun, even on a cloudless day, are insufficient for vitamin D synthesis and as a result many people become deficient in vitamin D during this period.
The mechanisms by which vitamin D improves cancer survival are not fully known however calcitriol, the biologically active form of vitamin D, has been found to inhibit cancer cell proliferation and increase apoptosis (programmed cell death). Several studies have found some impressive results when high dose calcitriol is combined with other cancer treatments. More information on calcitriol as a potential cancer treatment can be found here.
What should we make of all this? I would recommend that those who have recently been diagnosed with cancer should try to get at least two hours of direct sunlight a day and eat a range of foods rich in vitamin D such as salmon, shrimp, sardines, tuna, milk, eggs, and mushrooms. Daily supplementation of vitamin D should also be considered, either through cod liver oil, which contains 1350 IU of vitamin D per tablespoon, or a straight vitamin D3 supplement containing at least 5000 IU. The tolerable upper intake for vitamin D (the highest level at which adverse affects are unlikely) is currently set at 4000 IU for adults however short term intakes as high as 10,000 IU are unlikely to be harmful.
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